Many viruses suppress host antiviral responses through the global inhibition of host gene expression, often referred to as host shut-off. Vesicular stomatitis virus (VSV), the prototype rhabdovirus, is a well-established example of a virus that suppresses antiviral responses through the global inhibition of host gene expression. The host shut-off in VSV-infected cells is particularly extensive, resulting in the inhibition of hst transcription, nuclear-cytoplasmic transport of host mRNA, and translation of host proteins. The work of our laboratory and others has shown that the VSV matrix (M) protein is the major inhibitor of host gene expression in VSV-infected cells, and that the ability of M protein to inhibt host gene expression is genetically separable from its function in virus assembly. The goal of this project is to determine how a relatively small (229 a.a.) protein can have such a profound effect on host gene expression. M protein appears to inhibit host gene expression by binding to host components and interfering with their function. Thus far the only host component identified that binds to M protein and not to mutant M proteins is the RNA-binding protein Rae1. Rae1 is a multifunctional protein that was originally thought to be involved in mRNA transport. However, our recent experiments have shown that the M protein-Rae1 complex in VSV-infected cells primarily inhibits host transcription. Furthermore, silencing Rae1 expression has no effect on nuclear accumulation of host mRNAs induced by VSV infection, demonstrating that the block in their transport is independent of Rae1 expression. Finally, our data indicate that the inhibition o translation by VSV is a downstream effect of the inhibition of transcription, thus raising the question of how the virus counters this inhibition in order for viral mRNAs to be translated. The stimulation of translation of viral mRNAs appears to be due to an activity of M protein that is independent of its host shut-off function and involves novel assembly of ribonucleoprotein particles (RNP) that promote translation. The mechanisms by which M protein affects these three levels of gene expression will be determined according to the following aims: 1) Determine the mechanism by which M protein-Rae1 complexes inhibit host transcription. 2) Determine the role of host RNA-binding proteins in mRNA transport in VSV-infected cells. 3) Determine the role of M protein and host RNA-binding proteins in promoting the selective translation of viral mRNAs in VSV-infected cells. These experiments will use state-of-the-art chromatin and RNP immunoprecipitation approaches combined with high throughput sequencing to analyze host and viral gene expression in cells infected with well-characterized M protein mutants or cells in which expression of key host factors is suppressed by RNA silencing. These experiments should reveal novel mechanisms by which VSV inhibits host gene expression. In addition, they should provide novel information about how cellular RNA-binding proteins like Rae1 can regulate host transcription, and how networks of RNA-binding proteins can control translation that is applicable to other viruses that suppress antiviral responses by the global inhibition of host transcription and RNA transport.